src/runtime: add leveldb memhash

Author: dgryski

src/runtime/memhash_fnv.go

@@ -1,5 +1,5 @@
-//go:build !runtime_memhash_tsip
-// +build !runtime_memhash_tsip
+//go:build !runtime_memhash_tsip && !runtime_memhash_leveldb
+// +build !runtime_memhash_tsip,!runtime_memhash_leveldb
 
 package runtime
 

src/runtime/memhash_leveldb.go

@@ -0,0 +1,74 @@
+//go:build runtime_memhash_leveldb
+// +build runtime_memhash_leveldb
+
+package runtime
+
+import (
+	"unsafe"
+)
+
+func ptrToSlice(ptr unsafe.Pointer, n uintptr) []byte {
+	var p []byte
+
+	type _bslice struct {
+		ptr *byte
+		len uintptr
+		cap uintptr
+	}
+
+	pslice := (*_bslice)(unsafe.Pointer(&p))
+	pslice.ptr = (*byte)(ptr)
+	pslice.cap = n
+	pslice.len = n
+
+	return p
+}
+
+// leveldb hash
+func hash32(ptr unsafe.Pointer, n, seed uintptr) uint32 {
+
+	const (
+		lseed = 0xbc9f1d34
+		m     = 0xc6a4a793
+	)
+
+	b := ptrToSlice(ptr, n)
+
+	h := uint32(lseed^seed) ^ uint32(uint(len(b))*uint(m))
+
+	for ; len(b) >= 4; b = b[4:] {
+		h += uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
+		h *= m
+		h ^= h >> 16
+	}
+	switch len(b) {
+	case 3:
+		h += uint32(b[2]) << 16
+		fallthrough
+	case 2:
+		h += uint32(b[1]) << 8
+		fallthrough
+	case 1:
+		h += uint32(b[0])
+		h *= m
+		h ^= h >> 24
+	}
+
+	return h
+}
+
+func hash64finalizer(key uint64) uint64 {
+	key = ^key + (key << 21) // key = (key << 21) - key - 1;
+	key = key ^ (key >> 24)
+	key = (key + (key << 3)) + (key << 8) // key * 265
+	key = key ^ (key >> 14)
+	key = (key + (key << 2)) + (key << 4) // key * 21
+	key = key ^ (key >> 28)
+	key = key + (key << 31)
+	return key
+}
+
+func hash64(ptr unsafe.Pointer, n, seed uintptr) uint64 {
+	h32 := hash32(ptr, n, seed)
+	return hash64finalizer((uint64(h32^xorshift32(uint32(seed))) << 32) | uint64(h32))
+}